Ultrastructural Localization of Caspase-14 in Human Epidermis

Abstract

Caspase-14 has been implicated in the formation of stratum corneum because of its specific expression and activation in terminally differentiating keratinocytes. However, its precise physiological role and its protein substrate are elusive. We studied the ultrastructural localization of caspase-14 in human epidermis to compare its distribution pattern with that of well-characterized differentiation markers. Immunogold cytochemistry confirmed that caspase-14 is nearly absent in basal and spinous layers. In the granular, layer nuclei and keratohyalin granules were labeled with increasing intensity towards the transitional layer. Particularly strong caspase-14 labeling was associated with areas known to be occupied by involucrin and loricrin, whereas F-granules, occupied by profilaggrin/filaggrin, were much less labeled. A high density of gold particles was also present at the forming cornified cell envelope, including desmosomes. In corneocytes, intense labeling was both cytoplasmic and associated with nuclear remnants and corneodesmosomes. These observations will allow focusing efforts of biochemical substrate screening on a subset of proteins localizing to distinct compartments of terminally differentiated keratinocytes.

AKT1 Provides an Essential Survival Signal Required for Differentiation and Stratification of Primary Human Keratinocytes

“…Therefore, caspase 14 expression was determined by immunostaining. A suprabasal expression pattern of caspase 14 was observed in shSCRAM cultures, consistent with previous reports (27,29). Similar results were observed for shAKT2.…”

Acute Modulations in Permeability Barrier Function Regulate Epidermal Cornification

“…In contrast to other caspases, its activation does not require typical apoptotic stressors or stimuli. 57 The observation here that corneocytes in Casp14 Ϫ/Ϫ mice display strikingly attenuated cornified envelopes is consistent with immunoelectron microscopy studies that have shown localization of this enzyme in the vicinity of cornified envelopes, 58 suggesting together that Casp-14 regulates cornified envelope formation. Yet, although Casp-14 activation is both important for normal cornification and required for the transition of outer stratum granulosum cells into corneocytes after acute barrier perturbations, these studies did not define the physiological substrate(s) for Casp-14 nor did they exclude a role for other mechanisms, eg, stimulation of TNF and TRAIL activation, 59 -61 in the regulation of cornification.…”

Stratum corneum‐derived caspase‐14 is catalytically active

“…The antibody does not cross-react with other caspases as evidenced by the absence of bands: (i) on Western blots of total protein preparations from HeLa cells, which express caspases-1 to 10 and (ii) on protein preparations from non-differentiated keratinocytes, which express all human caspases except caspase-5 and caspase-14 (not shown). Preab-sorption of the antibody with purified recombinant caspase-14 prior to Western blot analysis of skin proteins prevents the appearance of bands at the size predicted for caspase-14 [18]. This confirms that the tissue-derived proteins that are recognized by the antibody are caspase-14 protein species.…”